Venturing where I may not belong: it seems very possible to me that
distances which otherwise would seem insurmountable to the foraging bee
would not be a barrier if wind conditions were right.  It would take only
a few bees to carry VM to uninfected colonies.  A colonizing swarm could
very well be dispersed and never manage to establish a viable family even
while individuals infiltrate and infect resident hives.

Anecdotal evidence for wind assisted dispersal (supported by the sudden
appearance of recognizable alien species) abound.

> Trevor Weatherhead noted:

> >We have a natural barrier by sea of 35 kilometres (about 22 miles) between
> >islands that the Asian bees (Apis cerana) from Papua New Guinea have not
> >breached.

Direction of seasonal prevailing winds would also be an important factor.

>    Santa Cruz Island, offshore from Santa Barbara, CA, has had Apis
> mellifera for more than 125 years (brought out by a beekeeper at that
> time).  Santa Rosa Island, less than 10 km west, has never had honey bees
> --- despite the short distance between those islands.

---------------
Richard Yarnell, SHAMBLES WORKSHOPS | No gimmick we try, no "scientific"
Beavercreek, OR. Makers of fine     | fix we attempt, will save our planet
Wooden Canoes, The Stack(R) urban   | until we reduce the population. Let's
composter, fly tying benches        | leave our kids a decent place to live.